Fig. 4: An example of a large, mature Class 2 structure. The kilometer-wide central band includes multiple lineaments symmetrical about the central groove, characteristic of Class 2. This lineament represents a spreading center, as evidenced by the alignment of features on the surrounding terrain upon reconstruction, which is consistent with our model of formation of Class 2 ridges as cracks ratcheted open during diurnal working. The lineament appears to have generated parallel side cracks, associated with crustal downwarping in our model, and some appear to have developed ridge structures, so that this lineament has begun to evolve into Class 3.